Agricultural harvesters are configured to sever crop plants from the ground, then to separate the grain portion of the crop plant from the other portions of the crop plant. The other portions of the crop plant are known as “MOG” (material other than grain).
One common way of performing this separation is to insert the cut crop material between a rotating cylinder (commonly called a “rotor”) and a stationary concave structure (commonly called a “basket” or “concave”. The rotor and the concave abut a layer of cut crop material that is inserted between them, and the relative motion between the two causes the grain portion to be broken loose (i.e. threshed) from the other portion of the crop plant.
Once threshed, the grain falls through apertures in the concave for further processing, and is ultimately saved in a grain tank (commonly called a “grain reservoir”) for later unloading from the combine.
The speed of the rotor with respect to the concave and the gap between the rotor and the concave, and the force applied to the cut crop material disposed between the rotor and the concave affect the amount of grain harvested and quality of the grain.
If the relative speed is too high, or the gap is too small, or the force applied to the cut crop material too high, the seeds can be damaged, and therefore the price the farmer can get for his grain in the marketplace. This is not economic.
If the relative speed is too low, or the gap too great, or the force too small, much of the grain may not be threshed and may be carried with the MOG and deposited on the ground. This reduces the yield of grain from a particular portion of the field and therefore reduces the amount of money the farmer makes. This is not economic.
Controlling the force applied to the grain compress between the rotor and the concave, and controlling the thickness of the crop mat (i.e. the gap between the rotor and the concave) are important to achieving the highest production possible from the combine.
One unfamiliar with modern agriculture would think that finding an optimum force and an optimum gap would be all that is required. This is not correct, however. Combines typically operate at a constant speed as they travel through the field harvesting crop. The crop, however, varies considerably. In some portions of the field the crop may be quite thin. In other portions of the field the crop may be quite thick. As a result, the amount of crop that is inserted between the rotor and the concave during harvesting can vary considerably.
The gap between the rotor and the concave should preferably change during harvesting to accommodate a thick or a thin crop mat between the rotor and the concave thereby accommodating the varying volumes of crop in different regions of an agricultural field.
Likewise, different crops require different rotor/concave gaps. Corn kernels, for example, are carried on a cob that is approximately 2 cm in diameter. In order to thresh ears of corn, a relatively wide gap is typically provided between the rotor and the concave. Soybeans, in contrast, are attached to stems, not cobs. They are typically provided a smaller gap (as compared to corn) to properly thresh the soybeans. Other crops have different optimum rotor/concave spacings.
Another difference between crops is the durability of the seed itself. Corn kernels may have a relatively thick, hard outer layer, and therefore may be able to withstand significant pressure without being damaged. Soybeans, may be more easily damaged and thus make tolerate less pressure without being damaged. Wheat, a long slender grain, may tolerate even less pressure without being damaged.
Thus, one rotor/concave spacing (i.e. one gap between the rotor and the concave) is not economically optimal for harvesting all crops under all harvesting conditions. Similarly, one amount of pressure applied to the crop mat is also not economically optimal for harvesting all crops under all harvesting conditions.
For this reason, modern combines permit the operator to set the pressure applied to the crop mat passing between the rotor and the concave as well as the thickness of the crop mat (i.e. the spacing between the rotor and the concave).
In several prior art arrangement (e.g. U.S. Pat. No. 3,974,837, GB1379808, EP0092599) a concave is biased against the rotor by springs.
In another prior art arrangement (U.S. Pat. No. 7,857,690) a controller maintains a constant set pressure in a hydraulic concave support system from a minimum separation distance to a maximum separation distance.
What is needed is an arrangement for controlling the force and gap between a rotor and a concave that is more responsive to different crop conditions and crops. It is an object of this invention to provide such a system.